function newImage(arg) {
            if (document.images) {
                        rslt = new Image();
                        rslt.src = arg;
                        return rslt;
            }
}

function changeImages() {
            if (document.images && (preloadFlag == true)) {
                        for (var i=0; i<changeImages.arguments.length; i+=2) {
                                    document[changeImages.arguments[i]].src = changeImages.arguments[i+1];
                        }
            }
}

var preloadFlag = false;

function preloadImages() {
            if (origOL) eval(origOL);
            if (document.images) {
                        home_over = newImage("images/nav/home_over.gif");
                        howItWorks_over = newImage("images/nav/howItWorks_over.gif");
                        features_over = newImage("images/nav/findNewCustomers_over.gif");
						process_over = newImage("images/nav/runCampaign_over.gif");
                        successStories_over = newImage("images/nav/precisionTargeting_over.gif");
						about_over = newImage("images/nav/aboutUs_over.gif");
						contactUs_over = newImage("images/nav/contact_over.gif");
                        home_on = newImage("images/nav/home_on.gif");
                        howItWorks_on = newImage("images/nav/howItWorks_on.gif");
                        features_on = newImage("images/nav/findNewCustomers_on.gif");
						process_on = newImage("images/nav/runCampaign_on.gif");
                        successStories_on = newImage("images/nav/precisionTargeting_on.gif");
						about_on = newImage("images/nav/aboutUs_on.gif");
						contactUs_on = newImage("images/nav/contact_on.gif");
						preloadFlag = true;
            }
}

// Get the original onload
var origOL = window.onload;

// Set onload to your function
window.onload = preloadImages;